Egg, fertilized egg, or embryo quality improving agent

ABSTRACT

Object of the present invention is to provide means for improving the quality of preimplantation embryos deteriorated with age or the like. The present invention relates to an agent for improving the quality of an egg, a fertilized egg, and/or an embryo, including a substance that inhibits signal transmission from CXCL5.

FIELD

The present invention relates to an agent for improving the quality ofan egg, a fertilized egg, and/or an embryo, including a substance thatinhibits signal transmission from CXCL5.

BACKGROUND

In general, cells constituting the human body repeatedly divide andproliferate as the body grows, and in such repetitions, cells areexposed to various stresses associated with aging and accumulate damage.This is considered to be due to oxidative damage due to accumulation ofactive oxygen, DNA damage due to ultraviolet rays, or the like,resulting in malfunction of mitochondria, dysfunction of intracellularmetabolism, or the like, leading to canceration/cell death. The factthat the quality of cell declines with age is thus a phenomenon commonto all mortal organisms including humans. Until now, it is inevitablethat the quality of cell deteriorates with age, and research fordelaying/stopping/improving deterioration of the quality of cell iswidely conducted.

In the field of reproductive medicine, attention is paid to the factthat the quality of preimplantation embryo deteriorates with age.Deterioration of the quality of preimplantation embryo leads to adecreased pregnancy rate or an increased miscarriage rate due toimplantation failure. Indeed, the incidence of infertility by age is 6%in the first half of the 20's, and starts to increase sharply in the30's, reaching 64% in the 40's. Among in vitro fertilization cases inJapan, 55% are aged cases of 38 years of age or older. While thepregnancy rate of in vitro fertilization cases of young patients is 26%on average, the pregnancy rate decreases in aged cases and is only 6.3%for cases of 38 years of age or older.

CXCL5 is a kind of chemokine, which contributes to chemotaxis/activationof neutrophils, and is known to be involved in inflammatory reaction(Patent Document 1).

PRIOR ART DOCUMENTS Patent Document

-   [Patent Document 1] Japanese Translation of PCT International    Application Publication No. 2005-527189

SUMMARY OF THE INVENTION Technical Problem

Attempts have been made to improve the quality of a preimplantationembryo deteriorated with age, but methods with high effectiveness havenot been developed. As a result, pregnancy is performed not by ownembryo, but by in vitro fertilization/embryo transplantation of an eggprovided by a young woman.

In such a pregnancy with an egg provided, an ethical problem is pointedout to fertilize an egg of another person and a sperm of a husband,transplant the preimplantation embryo into the uterus, and pregnant.There is also a view that immune abnormality occurs in a mother's bodyby pregnancy of a completely non-self child, and pregnancy complicationsincrease. Furthermore, egg donors also need to receive highly invasiveactions such as frequent injections and egg collection for ovarianstimulation, and safety problems are pointed out.

On the other hand, attempts have been made to improve the quality ofpreimplantation embryos by using supplements that may reduce oxidativestress and inflammatory damage, but scientifically proven highlyeffective supplements have not been found. In other words, means forimproving preimplantation embryos deteriorated with age or the like aredemanded.

In order to meet these demands, the present invention aims to providemeans for improving the quality of preimplantation embryos deterioratedwith age or the like.

Solution to Problem

The present inventors conducted intensive studies to solve theabove-described problems. As a result, it was found that CXCL5 which isa kind of chemokine induces aging of embryos, and found that inhibitionof signal transmission from CXCL5 can improve the quality ofpreimplantation embryo deteriorated due to age or the like. Based on thefindings, the present invention has been completed.

That is, the present invention relates to the following.

[1] An agent for improving a quality of an egg, a fertilized egg, and/oran embryo, including a substance that inhibits signal transmission fromCXCL5.

[2] The agent according to [1], wherein the substance that inhibitssignal transmission from CXCL5 is a substance that inhibits aninteraction between CXCL5 and CXCR2.

[3] The agent according to [2], wherein the substance that inhibits aninteraction between CXCL5 and CXCR2 is an anti-CXCL5 antibody or afragment thereof, an anti-CXCR2 antibody or a fragment thereof, or aCXCR2 antagonist.

[4] The agent according to any one of [1] to [3], wherein the quality ofan egg, a fertilized egg, and/or an embryo is deteriorated due to aging.

[5] A culture medium of an egg, a fertilized egg, and/or an embryo,containing the agent according to any one of [1] to [4].

[6] A method of predicting aging of an egg, a fertilized egg, and/or anembryo, including a step of determining a presence or absence of agingof an egg, a fertilized egg, and/or an embryo by using a concentrationof CXCL5 in a serum isolated from a subject as an index.

[7] A method of predicting aging of an egg, a fertilized egg, and/or anembryo, including a step of determining a presence or absence of agingof an egg, a fertilized egg, and/or an embryo using a concentration ofCXCL5 in an ovarian tissue isolated from a subject as an index.

[8] A method of improving a quality of an egg, a fertilized egg, or anembryo, including a step of bringing an egg, a fertilized egg, or anembryo into contact with a substance that inhibits signal transmissionfrom CXCL5.

[9] A method of culturing an egg, a fertilized egg, or an embryo,including a step of culturing an egg, a fertilized egg, or an embryo ina culture medium containing a substance that inhibits signaltransmission from CXCL5.

Advantageous Effects of the Invention

According to the present invention, by inhibiting CXCR2-mediated signaltransmission from CXCL5, the quality of an egg, a fertilized egg, or anembryo deteriorated due to aging or the like can be improved, andpregnancy rate/fertility rate in in vitro fertilized embryotransplantation or the like can be increased. Aging of an egg, afertilized egg, or an embryo can be predicted by using the concentrationof CXCL5 in blood or an ovarian tissue as a biomarker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing results of biological function analysis ofgenes whose expression was varied by gene expression comparison ofblastocysts of young infertile patients and elderly infertile patients.

FIG. 2 shows results of the blastocyst reaching rates of embryosobtained by using a CXCL5 neutralizing antibody, a CXCR2 antagonist, ora combination thereof.

FIGS. 3A and 3B show results of transplantation of embryos obtained byusing a CXCL5 neutralizing antibody and a CXCR2 antagonist incombination. A of FIG. 3 shows the implantation rate of mice in eachgroup. B of FIG. 3 shows the offspring acquisition rate of mice in eachgroup.

FIGS. 4A, 4B, 4C and 4D show results of transplant of embryos obtainedby adding a CXCL5 neutralizing antibody and a CXCR2 antagonist eachindividually. A of FIG. 4 shows the implantation rate of a CXCL5neutralizing antibody-added group. B of FIG. 4 shows the offspringacquisition rate of a CXCL5 neutralizing antibody-added group. C of FIG.4 shows the implantation rate of a CXCR2 antagonist-added group. D ofFIG. 4 shows the offspring acquisition rate of a CXCR2 antagonist-addedgroup.

FIG. 5 shows results of the blastocyst reaching rate of embryos obtainedby adding CXCL5 to young mice.

FIGS. 6A and 6B show results of transplant of embryos obtained by addingCXCL5 to young mice. A of FIG. 6 shows the implantation rate of mice ineach group. B of FIG. 6 shows the offspring acquisition rate of mice ineach group.

FIGS. 7A, 7B, 7C and 7D show results of expression levels of agingmarkers in embryos obtained by adding CXCL5 to young mice. A of FIG. 7shows the expression level of p21. B of FIG. 7 shows the expressionlevel of p53. C of FIG. 7 shows the expression level of PAI-1. D of FIG.7 shows the expression level of IL-6.

FIGS. 8A and 8B show measurement results of the concentration of CXCL5in serum and ovary of aged and young mice. A of FIG. 8 shows theconcentration in the serum. B of FIG. 8 shows the concentration in theovary.

DESCRIPTION OF THE EMBODIMENTS Quality Improving Agent

One embodiment of the present invention relates to an agent forimproving the quality of an egg, a fertilized egg, and/or an embryo,including a substance that inhibits signal transmission from CXCL5(hereinafter, sometimes simply referred to as “quality improvingagent”). In other words, the present invention is characterized in thata substance that inhibits signal transmission from CXCL5 is used forimproving the quality of an egg, a fertilized egg, and/or an embryo.“Improving the quality of an egg, a fertilized egg, and an embryo” canbe rephrased as “improving the pregnancy ability of an egg, a fertilizedegg, and an embryo.”

As shown in the Examples below, the present inventors revealed that theconcentration of CXCL5 in ovaries increases due to aging and the like.It was found that CXCL5 induces aging of an egg, a fertilized egg, anembryo, and the like, resulting in deteriorated quality of the embryo.Furthermore, it was found that the quality of an egg, a fertilized egg,or an embryo deteriorated by CXCL5 can be improved by inhibiting signaltransmission from CXCL5 via CXCR2 which is a chemokine receptor. Basedon the findings, the present invention has been completed.

In other words, the agent for improving the quality of an egg, afertilized egg, and/or an embryo of the present invention is a substancethat inhibits signal transmission from CXCL5, and is not particularlylimited as long as the substance exerts action of improving the qualityof an egg, a fertilized egg, or an embryo. Examples thereof include asubstance that inhibits an interaction between CXCL5 and CXCR2.

Examples of the substance that inhibits an interaction between CXCL5 andCXCR2 include an anti-CXCL5 antibody or a fragment thereof, ananti-CXCR2 antibody or a fragment thereof, and a CXCR2 antagonist. Thesecan be used alone or in combination of two or more kinds thereof.

Examples of the anti-CXCL5 antibody, anti-CXCR2 antibody or a fragmentthereof include an antibody (neutralizing antibody) that inhibits aninteraction between CXCL5 and CXCR2 by linking to CXCL5 or CXCR2 or afragment thereof.

As the anti-CXCL5 antibody and anti-CXCR2 antibody, a known one can beused. Although not particularly limited, examples of the anti-CXCL5antibody include Anti-CXCL5 antibody (abeam, R and D systems, LifeSpanBiosciences, ThermoFisher SCIENTIFIC). Although not particularlylimited, examples of the anti-CXCR2 antibody include Anti-CXCR2 antibody(abeam), Human CXCR2/IL-8RB Mab (R and D systems), Mouse MonoclonalCXCR2/IL-8 RB Antibody (Novuss Biologicals), CXCR2/IL8RB antibody(ThermoFisher SCIENTIFIC).

The anti-CXCL5 antibody can also be produced by a conventional methodusing CXCL5 or a fragment thereof as an antigen, and such an antibodycan be used in the present invention.

The anti-CXCR2 antibody can also be produced by a conventional methodusing CXCR2 or a fragment thereof as an antigen, and such an antibodycan be used in the present invention.

The antibody may be a polyclonal antibody or a monoclonal antibody.

The antibody may be a complete antibody molecule or an antibody fragmentcapable of specifically linking to an antigen, such as Fab (fragment ofantigen binding), F(ab′)2, Fab′, Fv, scFv (single chain Fv), dsFv(disulfide stabilized Fv), CDR (complementarity determining region). Ahuman chimeric antibody or a humanized antibody can also be used as theantibody.

Example of the CXCR2 antagonist include a substance that inhibits aninteraction between CXCL5 and CXCR2 by competing with CXCL5 and links toCXCR2 and does not itself have the ability to activate CXCR2.

As the CXCR2 antagonist, a known CXCR2 antagonist can be used. Althoughnot particularly limited, examples thereof include SB225002 (TOCRIS).

Antibodies and antagonists that inhibit an interaction between CXCL5 andCXCR2 preferably inhibit linking of CXCL5 and CXCR2 to 50% or less, 40%or less, 30% or less, 20% or less, 10% or less, or 1% or less ascompared with linking in the absence of antibody and antagonist.Antibodies and antagonists to be used in the present invention can beselected by a known method using CXCL5 and CXCR2 as indices as towhether or not to inhibit linking of CXCL5 and CXCR2. By inhibitinglinking of CXCL5 and CXCR2, CXCR2-mediated signal transmission fromCXCL5 is inhibited, and the quality of an egg, a fertilized egg, or anembryo deteriorated by aging or the like can be improved. Antibodies andantagonists used in the present invention also can be selected by aknown method using CXCL5 and CXCR2 as indices as to whether or not toinhibit CXCR2-mediated signal transmission from CXCL5.

By bringing the agent for improving the quality of an egg, a fertilizedegg, and/or an embryo of the present invention into contact with an egg,a fertilized egg, or an embryo, CXCR2-mediated signal transmission fromCXCL5 is inhibited, and the quality of an egg, a fertilized egg, or anembryo deteriorated by CXCL5 is improved. Examples of the method ofbringing the agent for improving the quality of an egg, a fertilizedegg, and/or an embryo of the present invention in contact with an egg, afertilized egg, or an embryo include a method of adding the qualityimproving agent of the present invention to a culture medium andculturing the egg, the fertilized egg, or the embryo in the same culturemedium. Improvement of embryo quality in the present invention includes:improvement of embryo quality by improving the quality of an egg and/ora fertilized egg by bringing the quality improving agent of the presentinvention into contact with the egg and/or the fertilized egg; andimprovement of embryo quality by bringing the quality improving agent ofthe present invention into contact with an embryo. Similarly, thequality improvement of a fertilized egg in the present inventionincludes: quality improvement of a fertilized egg by improving thequality of an egg by bringing the quality improving agent of the presentinvention into contact with the egg; and quality improvement of afertilized egg by bringing the quality improving agent of the presentinvention into contact with the fertilized egg.

A quality improvement action of an egg, a fertilized egg, or an embryoof the present invention can be confirmed when one or more evaluationitems related to pregnancy/childbirth such as a blastocyst reachingrate, an implantation rate, an offspring acquisition rate, or amiscarriage rate in a group to which the quality improving agent of thepresent invention is added in an in vitro culture system or the likewhich is usually used is improved compared with a group to which noquality improving agent is added.

The subject to which the agent for improving the quality of an egg, afertilized egg, or an embryo of the present invention is applied is notparticularly limited as long as the subject is a subject whose qualityof an egg, a fertilized egg, or an embryo is deteriorated due to agingor the like and which is demanded to be improved. Examples thereofinclude: a subject whose quality of an egg, a fertilized egg, or anembryo is deteriorated due to secretion or increased secretion of CXCL5with aging; and a subject whose pregnancy rate/fertility rate or thelike deteriorated due to such deterioration of an egg, a fertilized egg,or an embryo. The subject is a mammal and examples of the mammalinclude, but are not limited to, a human, and a non-human animal such asan animal having commercial value for meat and dairy production such asa pig, a cattle, a bovid, a horse, or a water buffalo.

Culture Medium

One embodiment of the present invention relates to a culture medium ofan egg, a fertilized egg, and/or an embryo containing an agent forimproving the quality of an egg, a fertilized egg, and/or an embryocomposed of a substance that inhibits signal transmission from CXCL5(hereinafter, sometimes simply referred to as “culture medium”). Theculture medium of an egg, a fertilized egg, and/or an embryo of thepresent invention is characterized by containing the agent for improvingthe quality of an egg, a fertilized egg, and/or an embryo of the presentinvention, and can be used to improve the quality of an egg, afertilized egg, and/or an embryo that is deteriorated due to secretionand increased secretion of CXCL5 with aging or the like during culturingthe egg, the fertilized egg, or the embryo.

The culture medium of the present invention is not particularly limitedas long as the medium contains the agent for improving the quality of anegg, a fertilized egg, and/or an embryo of the present invention as aneffective ingredient. For example, the culture medium of the presentinvention can be produced by adding the agent for improving the qualityof an egg, a fertilized egg, and/or an embryo of the present inventionto a known culture medium of an egg, a fertilized egg, or an embryo.

As the culture medium of an egg, a fertilized egg, or an embryo to beused for in vitro fertilization or the like, culture media of differentcompositions can be used depending on the stage of development or thelike. There is no particular limitation as long as the medium is aculture medium which is conventionally used for culturing an egg, afertilized egg, or an embryo, and the culture medium of the presentinvention can be produced by addition of the agent for improving thequality of an egg, a fertilized egg, and/or an embryo of the presentinvention. An embodiment in which the quality improving agent of thepresent invention is added to a culture medium used for culturing afertilized egg and a culture medium used for culturing an embryo fromthe morula stage to the blastocyst stage is preferable.

More specifically, a first culture medium used for culturing an embryofrom fertilization and postfertilization of a sperm and an egg(pronuclear stage) to 16 cell stage, a second culture medium used forculturing an embryo from the morula stage to the blastocyst stage, andthe like are used as a culture medium for an egg, a fertilized egg, oran embryo used for in vitro fertilization or the like. For the firstculture medium and the second culture medium, the same culture mediummay be used. For collection of a sperm and collection of an egg, thefirst culture medium can be used. These culture media are commerciallyavailable, and a commercially available culture medium can also be usedfor producing the culture medium of the present invention. Although notparticularly limited, as the first culture medium, in addition to aculture medium for laboratory animals, Sydney IVF Fertilization medium(Cook medical), Sydney IVF Cleavage medium (Cook medical), SequentialFert (ORIGIO), Sequential Cleav (ORIGIO), Universal IVF medium (ORIGIO),G-IVFTM (Vitrolife), G-1TM v5 (Vitrolife), or the like can be used, andas the second culture medium, in addition to a culture medium forlaboratory animals, Sydney IVF Blastosist medium (Cook medical),Seaquential Blast (ORIGIO), Blastassist medium (ORIGIO), G-2TM v5(Vitrolife), or the like can be used.

The culture medium of the present invention can also be produced using aculture medium prepared by dissolving an inorganic salt, a saccharide,an amino acid, a cytoprotective substance, an antibiotic, aphysiologically active substance, and the like in ultra pure ordistilled water or the like.

In the case of an antibody or a fragment thereof, the content of theagent for improving the quality of an egg, a fertilized egg, and/or anembryo of the present invention in a culture medium, as theconcentration in the culture medium, is usually from 0.01 to 100 μg/ml,and preferably from 0.1 to 10 μg/ml. In the case of an antagonist, thecontent can usually be from 1 to 100 nM, and preferably from 10 to 30nM. When an antibody or a fragment thereof and an antagonist are used incombination, the content can be usually from 28.6:1 to 2857.1:1, andpreferably from 28.6:1 to 1,000:1 (mass ratio).

Cultivation of an egg, a fertilized egg, or an embryo can be carried outaccording to a known culture method except that the culture medium ofthe present invention is used. Conditions for culturing are exemplifiedbelow, but the culture conditions are not limited thereto, and can beappropriately changed in accordance with an object to be applied, arequired effect, and the like.

Cultivation temperature can usually be 37° C. or higher. The culture gasphase can be a gas phase of usually 5% CO₂ and 95% O₂.

The culture time can be usually from 1 hour to 2 hours in the case ofpre-culture of an egg for in vitro fertilization, usually from 5 to 72hours in the case of a fertilized egg, and usually from 72 to 144 hoursin the case of an embryo after morula stage.

The quality improving agent of the present invention can be brought intocontact with an egg, a fertilized egg, or an embryo during at least oneof the period of preculture of an egg, the period of culture of afertilized egg, and the period of culture of an embryo at or after themorula stage.

The quality improving agent of the present invention may be brought intocontact with an egg, a fertilized egg, or an embryo over a plurality ofculture periods. The time for bringing the quality improving agent ofthe present invention into contact with an egg, a fertilized egg, or anembryo may be all or part of each period.

The culture medium of an egg, a fertilized egg, and/or an embryo of thepresent invention is not particularly limited, and is intended for anegg, a fertilized egg, and an embryo of a mammal requiring improvementof the quality of an egg, a fertilized egg, or an embryo that isdeteriorated due to aging or the like, improvement of declined successrate of in vitro fertilization/intracytoplasmic sperm injection by anegg, a fertilized egg, or an embryo, or the like. The subject is amammal and examples of the mammal include, but are not limited to, ahuman, and a non-human animal such as a pig, a cattle, a bovid, a horse,or a water buffalo.

Method of Predicting Aging

One embodiment of the present invention relates to a method ofpredicting aging of an egg, a fertilized egg, and/or an embryo,including determining the presence or absence of aging of an egg, afertilized egg, and/or an embryo by using the concentration of CXCL5 ina serum isolated from a subject as an index. Another embodiment of thepresent invention relates to a method of predicting aging of an egg, afertilized egg, and/or an embryo, including determining the presence orabsence of aging of an egg, a fertilized egg, and/or an embryo using theconcentration of CXCL5 in an ovarian tissue isolated from a subject asan index (hereinafter, each of the methods is sometimes simply referredto as “method of predicting aging”).

As shown in the Examples below, it was revealed that the concentrationof CXCL5 in an ovary correlated with the degree of the concentration ofCXCL5 in a serum. Therefore, in addition to using the CXCL5concentration in the ovary as an index, by using the concentration ofCXCL5 in the serum as an index, it is possible to predict theconcentration of CXCL5 in the ovary and whether or not an egg, afertilized egg, or an embryo is subjected to induction of aging byCXCL5.

Examples of blood used as a specimen in the present invention include aserum, and a serum can be appropriately obtained by treating bloodcollected from a subject according to a conventional method.

Examples of the ovarian tissue to be used as a specimen in the presentinvention include an ovarian tissue itself, an ovarian tissuepreparation, an ovarian tissue-derived component (an ovary cell, afollicular fluid, a granule membrane cell, or the like), and these canbe appropriately obtained by treating ovarian tissue collected from asubject according to a conventional method.

The concentration of CXCL5 in the ovarian tissue is not limited to theconcentration of CXCL5 protein, and may be the concentration of asubstance related to CXCL5 expression or the like. Here, the expressionmeans transcription of the gene of CXCL5 or translation from atranscription product of the gene.

The method for measuring the concentration of CXCL5 in a serum or anovarian tissue is not particularly limited, and examples thereof includevarious chromatographic methods such as an immunochemical method and anHPLC method. When the related substance is a nucleic acid, examples ofthe method for measuring the concentration of CXCL5 include a PCR methodsuch as a RT-PCR method. From the viewpoint of convenience and the like,it is preferable to measure by an immunochemical method using anantibody that recognizes CXCL5.

The immunochemical method used for measuring the concentration of CXCL5in a serum or an ovarian tissue is not particularly limited, andexamples of a known method include an enzyme immunoassay (EIA method), alatex agglutination method, an immunochromatography, a radioimmunoassay(RIA method), a fluorescence immunoassay (FIA method), a luminescenceimmunoassay, a spin immunoassay, a turbidimetric method for measuringthe turbidity associated with formation of an antigen-antibody complex,an enzyme sensor electrode method for detecting a potential change dueto linking with an antigen using an antibody solid phase membraneelectrode, an immunoelectrophoresis, and a Western blotting method. Fromthe viewpoint of convenience and the like, it is preferable to measureby an EIA method, a latex agglutination method, or animmunochromatography method.

The EIA method includes a competitive method of competing anenzyme-labeled antigen with an antigen in a specimen, and anoncompetitive method of not competing with each other, and among these,a sandwich enzyme-linked immune solid-phase assay (sandwich ELISA) whichis a non-competitive method using two kinds of antibodies is preferablein terms of ease of operation and the like.

When the concentration of CXCL5 in a serum or an ovarian tissue is usedas an index, for example, the concentration of CXCL5 in the serum orovarian tissue of the same type of control as a subject (such as ahealthy subject or a young subject) is set as a cutoff value, or acutoff value is set based on the concentration. The cutoff value can beappropriately set as the concentration of CXCL5 in a control serum or anovarian tissue or a value based on the concentration according to aspecimen, a required effect, or the like based on a conventional method.

When the concentration of CXCL5 in a serum or an ovarian tissue isolatedfrom a subject is higher than the cutoff value or a preset cutoff value,it is determined that the egg, the fertilized egg, or the embryo isaged. When the concentration of CXCL5 in a serum or an ovarian tissueisolated from a subject is the same as or lower than a cutoff value, itis determined that the egg, the fertilized egg, or the embryo is notaged. Aging thus can be predicted. The degree of aging can be predictedby comparing the concentration of CXCL5 in a serum or an ovarian tissueisolated from a subject to a cutoff value.

The object of application of the method of predicting aging of thepresent invention is a mammal, and is not particularly limited. Themammal is not particularly limited, and examples thereof include ahuman, and a non-human animal such as a pig, a cattle, a bovid, a horse,or a water buffalo.

Quality Improvement Method and Culture Method

Furthermore, the present invention includes a method for improving thequality of an egg, a fertilized eggs, or an embryo, including a step ofcontacting the egg, the fertilized egg, or the embryo with a substancethat inhibits signal transmission from CXCL5. The present inventionincludes a method for improving the quality of an egg, a fertilized egg,or an embryo and increasing the pregnancy rate/fertility rate, includinga step of bringing the egg, the fertilized egg, or the embryo intocontact with a substance that inhibits signal transmission from CXCL5.For the contact method or the like, the contents of the above sectioncan be referred to.

Furthermore, the present invention includes a method of culturing anegg, a fertilized egg, or an embryo, including a step of culturing theegg, the fertilized egg, or the embryo in a culture medium containing asubstance that inhibits signal transmission from CXCL5. For theconditions of cultivation or the like, the contents of the above sectioncan be referred to.

EXAMPLES

Hereinafter, the present invention will be described in detail withreference to Examples, but the present invention is not limited to thefollowing Examples.

Example 1

Gene expression profiles were compared in preimplantation embryos ofyoung infertile patients and preimplantation embryos of elderlyinfertile patients of 39 years of age or older, and genes that differedin expression were comprehensively analyzed. Among them, those which aresecretion factors and which are highly expressed in elderly patientswere searched and used as candidate factors involved in deterioration ofthe quality of embryo due to aging. Specifically, an experiment wascarried out as follows.

Gene expression of blastocysts in young patients and elderly patientswas comprehensively compared by DNA microarray, and as a result, therewere 3,789 differentially expressed genes of 5 times or more inexpression level. As a result of biological function analysis of thesegenes, genes involved in metabolism, cell cycle, or the like wereaffected by aging (FIG. 1 ).

From among differentially expressed genes, those which were secretionfactors and which were highly expressed in elderly patients wereextracted, and CXCL5 showing expression levels 202.8 times higher inblastocysts of elderly patients compared with young patients wasregarded as an eventual candidate factor.

Example 2

Whether the candidate factor CXCL5 obtained in Example 1 improved thequality of embryo deteriorated by aging by addition of a neutralizingantibody or an antagonist of a specific receptor in an in vitro culturesystem of an aged mouse embryo or not was examined. Ovulated mature eggswere collected from 42-week-old aged mice and subjected to in vitrofertilization, the obtained fertilized egg (zygote) was in vitrocultured using a culture medium to which a neutralizing antibody of acandidate factor or an antagonist of a specific receptor was added, andthe blastocyst reaching rate was determined in order to verify embryodevelopment ability. The obtained blastocysts were embryo transplantedinto pseudopregnant mice, for which the implantation rate and theoffspring acquisition rate were examined, and the quality of embryos wasfurther evaluated. Specifically, the experiment was carried out asfollows.

Laboratory Animal

ICR female mice (CLEA Japan, Inc., Tokyo, Japan) were used as laboratoryanimals. The mice were bred at a room temperature of 22° C. and ahumidity of 55% under light and dark environments every 12 hours. MFcontrol diet (Oriental Yeast Co., ltd., Tokyo, Japan) was given 6 g permouse per day. Water was allowed to be freely ingested at any time.3-week-old mice were used as young mice, and 42-week-old mice were usedas aged mice. Five mice were used in each group.

Handling and breeding of all mice conformed to standards of experimentalanimal facilities of St. Marianna University School of Medicine.

In Vitro Fertilization and Embryo Culture

Mice past 3 weeks and 42 weeks of age confirmed the sexual cycle byvaginal smear. 10 IU of gonadotropin (ASKA Pharmaceutical. Co., Tokyo,Japan) was intraperitoneally administered at the time of proestrus.Cumulus oocyte complexes (COCs) were collected from a fallopian tube 15hours after administration, and precultured for 30 minutes in 100 μl TYHmedium (LSI Medience corporation, Tokyo, Japan). Meanwhile, ICR malemice (10-12 weeks old) were subjected to general anesthesia withsomnopentyl anesthetic (Kyoritsuseiyaku Corporation, Tokyo, Japan), andcauda epididymis was extracted. A portion of the cauda epididymis wasincised, and the internal sperm was extruded and collected. Thecollected sperm mass was submerged in a 1.5 mL microtube containing 400μl TYH medium, and was subjected to swim up for 10 minutes in a CO₂incubator (37° C., 5% CO₂, 95% in air). Sperm after swim up was added to100 μl TYH medium containing COCs to an eventual concentration of2-3×10⁵/ml and cultured in CO₂ incubator (37° C., 5% CO₂, 95% in air)for 5-6 hours. After culturing, the sperm was removed from the egg in 30μl KSOM Medium (Merck Millipore, Darmstadt, Germany), and the number of2 cell stage embryos was calculated at that time. A young mouse controland an aged mouse control were then transferred to another 30 μl KSOMMedium, and cultured in a CO₂ incubator for 4 days. Drug treatmentgroups were transferred to Ill of KSOM Medium supplemented with a CXCL5neutralizing antibody (ab135203, abcam) with eventual concentrations of0.1 μg/ml, 1 μg/ml, and 10 μg/ml, 30 ml KSOM Medium supplemented with aCXCR2 antagonist (2725, TOCRIS) with eventual concentrations of 10 nMand 30 nM, and 30 μl KSOM Medium supplemented with a CXCL5 neutralizingantibody and a CXCR2 antagonist, and cultured for 4 days in a CO₂incubator. The blastocyst reaching rate was calculated as the number ofblastocysts/the number of two cell stage embryos.

Neutralizing antibodies of CXCL5 and antagonists of specific receptorswere added to fertilized eggs of aged mice at different concentrations,and no significant difference was observed between the control group andthe drug treated group on the blastocyst reaching rate (FIG. 2 ).

Embryo Transplantation and Caesarean Section

After culturing for 4 days, an embryo reaching a blastocyst stage embryowas transplanted. Recipient mice were ICR female mice of 6 to 10 weeksof age, and mated with ICR male mice vasoligated on the day before aharvesting day, and an individual whose vaginal plug could be confirmedthe next day was used. General anesthesia was given with somnopentylanesthetic, and the uterus was exposed by a back dorsal incision. Theuterus was fixed with tweezers, a 30 G injection needle (Dentronics,Tokyo, Japan) was drilled at an oviduct joint, a glass capillary withblastocyst aspirated was inserted, and the embryo was transplanted intothe uterus. After transplantation, the uterus was carefully returned tothe body, and the retroperitoneum and the skin were sutured. At the timeof transplantation, blastocysts obtained from mice of each group weretransplanted into recipient mice for each individual. Cesarean sectionwas carried out on the 19th day with the next day of egg collection asthe first day. Recipient mice were euthanized and underwent laparotomy,and the uterus was extracted and the fetus was removed. Implantationrate was calculated as the number of implantation traces/the number ofembryo transplantations, and the offspring acquisition rate wascalculated as the litter size/the number of implantation traces.

When blastocysts in the control group and the drug treated group weretransplanted into pseudopregnant mice, the implantation rate wasconsiderably improved in the neutralizing antibody+antagonist-addedgroup (One-way ANNOVA followed by Tukey-Kramer test, *P<0.05 vs.control, FIG. 3 ). Significant difference was observed between the agedcontrol and the neutralizing antibody (10 μg/ml)+antagonist (10 nM)added group. The offspring acquisition rate significantly increased inthe neutralizing antibody (10 μg/ml)+antagonist (10 nM)-added group(FIG. 3 ).

Even in the group to which only the neutralizing antibody (10 μg/ml) wasadded and the group to which only the antagonist (10 nM) was added, boththe implantation rate and the offspring acquisition rate tended to behigher in the drug treated group (FIG. 4 ).

Example 3

In the in vitro culture system of young mouse embryo, whether or notthere was a change in blastocyst reaching rate, implantation rate,offspring acquisition rate by adding the candidate factor was examinedusing a similar method to Example 2. Expression in the embryos of agingmarkers p16, p21, p53, PAI-1, and IL-6 was measured, and whether or notcell aging was induced was investigated. Specifically, the experimentwas carried out as follows.

Based on the method described in Example 2, in vitro fertilization andembryo culture were performed on young mice. Note that the control groupwas transferred to 30 μl KSOM Medium, the drug treated group wastransferred to 30 μl KSOM Medium supplemented with CXCL5 (ab9803, abcam)heat-denatured (95° C., 5 min) at an eventual concentration of 1,000 nMand CXCL5 at eventual concentrations of 100 nM, 300 nM, 1,000 nM, andcultured in a CO₂ incubator for 4 days. The blastocyst reaching rate wasthen calculated.

CXCL5 and heat-denatured CXCL5 were added to fertilized eggs of youngmice and cultured. As a result, the blastocyst reaching rate was notsignificantly different from the non-added control group (FIG. 5 ).

Based on the method described in Example 2, blastocysts of the controlgroup and the drug treated group were transplanted into pseudopregnantmice. The implantation rate and the offspring acquisition rate were thencalculated.

When blastocysts obtained by adding CXCL5 and heat-denatured CXCL5 weretransplanted into pseudopregnant mice, the implantation rate decreasedin the group to which CXCL5 was added (One-way ANNOVA followed byTukey-Kramer test, *P<0.05 vs. control, FIG. 6 ). In the group to whichCXCL5 was added at 1,000 nM, a significant difference was observed withthe non-addition control group. There was no significant difference inthe offspring acquisition rate with the control group (One-way ANNOVAfollowed by Tukey-Kramer test, * P<0.05 vs control, FIG. 6 ). There wasno significant difference between the heat-denatured CXCL5-added groupand the control group in both the implantation rate and the offspringacquisition rate.

Expression levels of aging markers (p16, p21, p53, PAI-1, IL-6) inembryos to which CXCL5 was added (n=30) were measured using RealtimeRT-PCR. Although there was no significant difference in the expressionlevel of p16, there was a significant increase in expression level ofp21, p53, PAI-1, IL-6 (T-test, * P<0.05 vs control, FIG. 7 ).

Example 4

Concentrations of candidate factors in young and aged mice were measuredin a serum and an ovary tissue, and whether or not the candidate factorswere useful as a biomarker capable of predicting aging of an embryo wasevaluated. Specifically, the experiment was carried out as follows.

Prior to in vitro fertilization in Example 2, a serum and an ovariantissue were collected for young mice and aged mice, respectively. Theconcentrations of CXCL5 in the serum and the ovary were measured usingELISA. The concentration of CXCL5 in the serum and the ovary of agedmice was significantly higher than that in young mice (T-test, * P<0.05vs control, FIG. 8 ). The tendency of the concentration of CXCL5 in theserum correlated with the tendency of the concentration of CXCL5 in theovary, and it was found that the concentration of CXCL5 in the ovary canbe predicted from the concentration of CXCL5 in the serum.

It was found that inhibition of CXCL5-CXCR2 signal in aged embryoimproved the quality of an egg, a fertilized egg, and an embryodeteriorated due to aging, and had an action for increasing thepregnancy rate and fertility rate in in vitro fertilized embryotransplantation or the like. It was found that CXCL5 induced aging of anembryo, and the concentration thereof in the serum was useful as anaging marker for an egg, a fertilized egg, and an embryo.

INDUSTRIAL APPLICABILITY

The present invention can be applied to medicines, medical devices,research reagents and the like.

1-7. (canceled)
 8. A culture medium of an egg, a fertilized egg, and/oran embryo, comprising a substance that inhibits signal transmission fromCXCL5.
 9. The culture medium according to claim 8, wherein the substancethat inhibits signal transmission from CXCL5 is a substance thatinhibits an interaction between CXCL5 and CXCR2.
 10. The culture mediumaccording to claim 9, wherein the substance that inhibits an interactionbetween CXCL5 and CXCR2 is an anti-CXCL5 antibody or a fragment thereof,an anti-CXCR2 antibody or a fragment thereof, or a CXCR2 antagonist. 11.The culture medium according to claim 8, wherein the culture medium isused for improving a quality of an egg, a fertilized egg, and/or anembryo.
 12. The culture medium according to claim 11, wherein thequality of an egg, a fertilized egg, and/or an embryo is deteriorateddue to aging.